A. Field of the Invention
The invention relates to a differential speed reducer device and particularly concerns a differential speed reducer device which is capable of ensuring a high reduction ratio without sacrificing compactness so as to respond to industrial needs.
B. Description of the Prior Art
In modern robot technology incorporated into various kinds of machine tools, a speed reducer has been associated with an electric motor to reduce its speed for application to a transfer arm. Examples of presently known speed reducers are worm wheel reducers, cyclo reducers, and harmonic drive reducers.
However, it would be desirable to have a speed reducer improved in the following respectsL (i) high reduction ratio with compact structure, (ii) high precision control with least idle play such as backlash action, (iii) elevated rigidity with high meshing rate, (iv) improved controllability with a relatively small inertia force at rotary members, and (v) minimum loss of torque with minimum wear.
A reducer device which provides these advantages (v) is shown in U.S. Pat. No. 4,829,851. In this patent, first and second discs are provided. Each surface has a groove defined by a cycloidal-based curve. A plurality of balls roll along each groove of the first and second discs when a rotational movement is transmitted to the second disc so as to impart the second disc with a nutational movement. A rectifier disc picks up a rotational movement from the nutational movement of the second disc to produce a reduced output.
It is, however, often desired to ensure a greater reduction ratio (up to 1/50.about.1/100) in a reducer device particularly employed to machine tools. From the point of strength and machinability, it is thought to be difficult for the prior reducer to ensure such a great reduction ratio without sacrificing its compactness.
Therefore, it is an object of the invention to provide a differential speed reducer device which enables high precision control with minimum backlash play, high rigidity with high meshing rate, improved controllability with small inertia force, and a greater reduction ratio with a compact structure.